Abstract Inadequate sleep ? either due to insufficient duration or poor quality ? has far-reaching consequences for health and well-being. Cognitive and physical functioning ? domains that are salient for older adults ? are especially sensitive to inadequate sleep. There is evidence that cognition and physical functioning are intertwined; gait, balance, and risk of falls have been directly linked to executive function, a cognitive domain that is particularly susceptible to impairment due to processes of aging. The Wisconsin Sleep Cohort (WSC) study is an ongoing longitudinal investigation of sleep and sleep disorders that has followed a population-based cohort of adults at approximate 4-year intervals since the late 1980s. Cohort subjects are now approximately 60-90 years old. We will use new and existing data?spanning up to 30 years? from a subsample (N~640) of the Wisconsin Sleep Cohort study to investigate the impact of exposure to unhealthy sleep duration and poor sleep quality throughout midlife as predictors of accelerated declines in key domains of cognitive and physical functioning in older age. WSC subjects have been comprehensively characterized on multiple dimensions of objectively- and subjectively-measured sleep, as well as multiple measurements of cognition from a comprehensive neurocognitive test battery and a measure of gait and balance. Following an 8- to 10-year interval since last studied, we propose to reassess this subsample of WSC subjects to collect additional data on these cognitive and physical functioning outcomes of aging. Specifically, we will: measure associations of exposure to unhealthy sleep duration (i.e., too short or too long) and disturbed sleep (e.g., lower sleep efficiency, more frequent arousals, greater sleep time variability) across midlife with cognitive decline and dementia in older age (Aim 1); and measure associations of exposure to unhealthy sleep duration and poor sleep quality across midlife with fall injuries and declines in gait and balance in older age (Aim 2). The WSC is the only study that has up to 30 years of longitudinal data that comprehensively characterize sleep, cognition, and physical functioning with repeated measures across midlife and into older adulthood. The WSC?s rich data set also includes a broad set of other pertinent variables, collected longitudinally, that can be investigated or controlled for. Sleep habits and characteristics are potentially modifiable factors that are likely to have a substantial impact on how adults age, experience quality of life, maintain independence, and contribute to the medical and caregiving burden in the US.